yes that is expected and not tunable in 3.1.x with configurations only. in 3.1.x the scheduler service (like all other services used by jbpm) are pluggable. so you could build your own scheduler service that e.g. leverages ejbtimer service.

that is exactly what we did added in 3.2.GA, which was just released. in 3.2, the pojo implementation is now multithreaded. and there is also an enterprise service implementation that maps to the enterprise services for async messaging and timers.

there is one known limitation with the enterprise services. because of a limitation in the ejb timer spec, we have to loop over all the timers in case we want to delete one by name during process execution. that might not scale very well in some situations. we are going to work out a solution for this in the next version (by replacing the usage of the timer service of one single SLSB with one entity bean per timer)

hope this gives you some insight